The influence of combination of surface roughness and nanostructure of adhesive on the strength of adhesively bonded joints

Abstract

Nowadays, adhesively bonded joints are frequently employed in engineering designs as they enable the manufacture of joints with great strength while remaining light. These joints used in aviation sectors, where lightness and reliability are important, are generally designed to join metal-metal, metal-composite and composite-composite adherends. The surface roughness of the adherends with its degree and the way the adhesive interacts with the surface are the most crucial parameters in these applications. In the current work, surface roughness and normal stress strength of nano-composite adhesive in butt joint subjected to tensile loading were investigated. DP460 liquid structural epoxy from 3 M was used as adhesive, AA2024-T3 aluminum alloy as adherend, Graphene-COOH and Carbon Nanotube-COOH as nanostructures while sandpaper and sandblasting methods were used for introducing roughness to the adherend surfaces. A two dimensional axisymmetric FE model was developed to get an insight about the joint failure. When the failure load obtained from experiments was examined, an increasing trend in maximum force values was noticed with an increase in surface roughness, but this increase in joint strength decreased when the surface roughness increased to very high values. In addition, minimum surface roughness reduces the adhesive's adhesion to the surface, thus reducing the normal stress strength of the joint. When 1 % Graphene-COOH nanostructure was added to the adhesive, the ultimate normal stress of the joints increased from 9 % to 21 %. However, when the same percentage of Carbon Nanotube-COOH was added, the increase was from 27 % to 62 %. Different normal stress values of the joints were obtained using by sanding and sandblasting methods even though the roughness resulting from the two treatments was similar.